The majority of current heavy vehicle brake systems use compressed air to apply the brakes. In such systems, control signals are typically transmitted from the driver of the vehicle to the control valves of the brake system, and the brakes are applied. These types of brakes are generally divided into two categories: service brakes and parking brakes. Service brakes are used primarily to slow the vehicle to a stop when the vehicle is moving. Parking brakes are used primarily for helping to prevent the vehicle from moving from a parked position, and may also be used in an emergency situation to slow a moving vehicle when the service brakes have failed, in order to provide a redundant brake circuit.
For service brakes, an operator generally depresses a brake pedal, which in turn actuates a control valve, allowing air pressure to travel to the brake, and the brake is applied. The parking brake is generally engaged by a vehicle operator by actuating a push/pull hand lever within the cab of the vehicle, located on the vehicle dash. The parking brake is generally a spring brake which is normally engaged, meaning that air pressure must be applied to the parking brake in order to release it. Thus, when there is no air pressure present, the parking brake is applied. Accordingly, if a vehicle loses air pressure (i.e., ruptured hose, failed component, etc.), and thus loses service brake air pressure and the ability to apply the service brakes, the parking brake will automatically engage, and act to slow a moving vehicle. Likewise, when the vehicle is parked and/or not in use, the parking brake can be engaged by the operator, helping to prevent the vehicle from moving from a parked position.
As mentioned above, typical current day heavy vehicles have a push/pull knob located in the cab of the vehicle which is used to engage and disengage the parking brake. A vehicle may have more than one push/pull knob, depending upon whether there is an additional control for the parking brakes on a trailer attached to the vehicle. The push/pull knob is generally connected to a push/pull double check (PPDC) valve, which controls the flow of air to the parking brake. Generally, when an operator pushes the valve in, it acts to provide air pressure to the parking brake, and thus release the brake, allowing the vehicle to move. In order to apply the brake, the operator pulls the push/pull knob, thus removing air pressure from the parking brake and causing it to engage. Generally, when the knob is pushed in, the air pressure acts to engage the knob and keep it in the pushed in position. Such push/pull knobs also have a feature which allows a manual override where, even if there is a failure in the air system, or the air pressure is not high enough to engage the push/pull knob, the operator may manually hold the knob in to disengage the parking brake and move the vehicle a short distance. In more current systems, the in-dash PPDC valve is replaced by a solenoid disposed away from the dash, which solenoid receives electronic control signals from a push button, switch, or the like which is disposed within reach of the vehicle driver (e.g., on the dash of the vehicle).
While many different systems which operate in a manner similar to that described above are known, all known prior art systems suffer from a number of disadvantages. One of such disadvantages relates to the complexity of such systems. Although not fully described above, typical heavy vehicle brake systems do not employ only a PPDC valve, but rather also include several additional components and valves, such as a manifold, an inversion valve, an anti-compounding valve, a relay valve, and possibly others (such as valves used in conjunction with electronic lift axle or steer axle applications, for example). Such systems often require a significant amount of plumbing running in a complex web to connect the various system components. Not only is this large amount of plumbing expensive, heavy and relatively difficult to install (thereby requiring a relatively large amount of time to install), but the potentially long lengths of plumbing between components can lead to delays in achieving required system pressures, such that, for example, parking brake release timing is increased.
These disadvantages have been addressed to some extent in certain prior art systems, such as those disclosed in U.S. Pat. Nos. 4,128,276 and 6,135,574 which disclose combination brake control/valve units having a so-called “modular” configuration. What is meant by “modular” in these prior art references is that various components of the brake control/valve units may be added, removed, swapped, etc. without replacing the entire unit. Thus, for example, if a particular desired functionality is desired, a module for achieving that functionality may be added to the unit. Similarly, if a functionality is not required, the module for achieving that functionality may be removed. Moreover, if a module is damaged or otherwise becomes inoperative, that module may be replaced without requiring replacement of the entire unit.
While such arrangements do provide some benefits over the systems described above which are based upon a plurality of spatially separated valves connected via a network of plumbing, they do suffer from disadvantages of their own. A major disadvantage of such arrangements is that while modules may be separately added to, removed from, or replaced within the core brake control/valve unit, each of the modules does rely on the core unit to operate (i.e., the modules are not standalone units which can operate independently of one another). Thus, for example, suppose that a core brake control/valve unit in accordance with the prior art is designed to be capable of operating ten modules. The core unit would necessarily be sized such that it could receive all ten modules. However, also suppose that based upon the particular application, only two modules are desired. In such a case, a large majority (i.e., eight tenths) of the core unit would be empty and would be taking up space and weight needlessly. The core unit would also likely be much more expensive than necessary. Now suppose that only one module was required for a particular application. Since each module relies upon the core unit to function, the single desired module could not be used by itself, but instead would have to be installed in the core unit, in a very inefficient manner from space, weight and cost standpoints.
What is desired, therefore, is a pneumatic brake system for heavy vehicles which does not require a significant amount of plumbing running in a complex web to connect various system components, which does not require plumbing that is expensive, heavy and relatively difficult to install and which can be installed relatively quickly, which does not suffer from long delays in achieving required system pressures such that parking brake release timing is satisfactory, which includes modular stand-alone components so that components of the system having different functionality may be directly joined together to form an integrated valve unit, and which is scalable and customizable in size as dictated by the application in which the system is to be used.